PT846092E - AQUOSA SOLUTION OF RUTENEOUS CHLORIDE FOR THE ENGRISHMENT OF CERAMIC SURFACES - Google Patents

Abstract

PCT No. PCT/EP97/03087 Sec. 371 Date Apr. 30, 1998 Sec. 102(e) Date Apr. 30, 1998 PCT Filed Jun. 13, 1997 PCT Pub. No. WO97/49650 PCT Pub. Date Dec. 31, 1997An aqueous ruthenium chloride solution for blackening ceramic surfaces includes ruthenium chloride; water present in an amount effective to provide an aqueous solution of ruthenium chloride; and a buffer which is selected from the group consisting of sodium acetate, sodium propionate, potassium acetate, potassium propionate, and mixtures thereof, and which is present in an amount effective to provide the aqueous solution with a pH of at least 1.5. A method for dyeing a ceramic surface includes applying the aqueous solution of ruthenium chloride to a ceramic surface by at least one of spraying, dipping, painting and printing to provide a treated surface; drying and firing the treated surface at a temperature ranging from about 300 to about 1400 DEG C. for a period of time ranging from one half hour to five hours; and grinding and polishing the treated surface to even out the treated surface.

Description

SHICO

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF RUTHIUM CHLORIDE FOR THE SUGGESTMENT OF CERAMIC SURFACES " The invention disclosed herein relates to blends for the coloring of black of ceramic products by the use of aqueous solutions of ruthenium compounds.

It is known that ruthenium chloride, in aqueous solution, can be employed to color from black-ash to porcelain. To this end, an aqueous solution of ruthenium chloride of high acidity is applied to the pieces, and is baked, whereby the chloride decomposes and the ruthenium oxide remains as thin as possible, silicic acid or, respectively, with the alumina of the parts and forming the colored pigments (see: Ullmann, Enzyklopâdie der technischen Chemie, 2nd edition, Vol. 4, pages 837 and 838).

It is known from the Czech Patent Application CS 248 541 B1 that ruthenium oxide, when in crystalline zirconium silicate networks, has a black-gray color such that said compounds can be used as black pigments.

In EP 0 704 411 AI it is further described that the salt or complex of ruthenium with carboxylic polyacids has a dark gray color (described as " black "), when application to parts of ceramic, when these are pre-treated with water (activated), then colored with the ruthenium solution and ending with a subsequent treatment with water. This process also leads, however, only to a darkening -

but never to a true coloration of black.

Thus, the problem arises of finding means with which the ceramic surfaces could be colored deep black, easily and economically.

This problem is solved by the features of the main claim and is complemented by the features of the secondary claims.

The solutions according to the invention consist of a commercial aqueous solution of ruthenium chloride, which usually contains a certain excess of mineral acid for stabilization. This aqueous solution is buffered with sodium and / or potassium acetate or propionate at a pH of at least 1.5, especially > 2, whereby these solutions are also kept stable for a longer period of time.

The solution is adjusted, in this case, to a ruthenium concentration of 0.1 to 10% by weight, necessitating for the buffering correspondingly large amounts of, eg, sodium acetate, according to the excess acid in the same way, concentrations of the order of magnitude of 0.1 to 10% by weight are normally employed.

The solutions according to the invention are applied by the normal spraying, immersion, painting, printing, etc. procedures on the ceramic objects to be colored, whereby amounts between 0.1 and 5 g / cm 2 are sufficient for coloring.

After drying, the ceramic objects are cooked in a suitable oven at a temperature between 1300 and 1400 ° C. For the decomposition of ruthenium compounds, temperatures between 800 and 1200 ° C, especially 1140 ° C, are preferred. The cooking time is between half an hour and five hours, preferably one and two hours. During this time, the -2-

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ruthenium compounds are pyrolyzed and the ruthenium oxide is formed in finely dispersed form. By suitable mineralizers such as fluorides and alkali chlorides, fluorsilicates, etc., as well as the addition of molybdenum or tungsten compounds, color perception can be promoted in a known manner.

[0011] The color perception obtained after cooking is determined objectively with the aid of a La * b * system. In this system " L " represents the brightness, while " a * " and " b * " correspond to both color tonality and color saturation. " a * " describes, in this case, the position on a red-green axis and " b * " the position on a yellow-blue axis.

Up to now, it has not been possible to determine on what basis the color depth of the buffered system according to the invention is essentially based on the unbuffered systems. Possible explanations may relate to differences in the size and / or size of ruthenium oxide particles separated from the buffered solution relative to the unbuffered solution. Another possibility could be that, during the evaporation of the un-buffered mineral acid during the pyrolysis, a certain granulation of the surface of the ceramic occurs, which would result in an additional light scattering and thereby impart a " hue gray ". On the other hand, it also appears that mineral acid has an important influence and not only the pH value of the solution is a decisive factor, since, for example, ruthenium complexes with organic polycarboxylic acids such as polyacrylates or copolymers of vinyl ether with maleic acid, known from the abovementioned EP 0 704 411, in fact, form stable complexes at pH values > 2, but only lead to the formation of dark gray colorations when baking. It is thus conceivable that, in the case of cooking from sodium acetate and chloride, sodium chloride is formed, which is responsible as a mineralizer for color formation. The solutions according to the invention penetrate the surface of the ceramic parts to a depth of 0.5 to 2 mm, the depth of penetration being further influenced in a known manner by means of glycerol, glucomannan, sugar and others, and provide an upper surface of a corresponding dark color by cooking.The organic substance is calcined to CO2 and H2 O. Irregularities and roughness of the surfaces can finally be equalized from In the same way by grinding, in a known manner, as long as they are no more polished than the penetration depth of the corresponding dyeing solution. The solution itself drips relatively little during application, so that a clear contour printing is also possible such as, for example, in the screen printing process. With coloring solutions known in other colors, It is also in this way to produce compositions of decorative designs.

The following examples describe the process according to the invention in more detail, without having to limit it.

Example 1 A solution of ruthenium chloride is buffered to pH 2 with sodium acetate and adjusted to 6% by weight ruthenium.

With the aid of a sprayer, this solution is sprayed onto the top side of white ceramic tiles with 5 x 5 cm of edge length, until the weight of the plaque has increased by 0.2 g. The tiles are then dried in a drying oven at 100 ° C and then brought to the baking oven where they are held for 6 hours at 600 ° C before the temperature is raised to 1140 ° C within the range of one hour and held at this temperature for another hour, after which the plates are cooled slowly. The surfaces of the plates are then polished until smooth. After the above described cooking process, the following color values are obtained on the surfaces of the tiles: L * a * b * V & B tiles, test No. 38.26 -2.42 CM 1 Tiles V & B, Test No. 2 36, 97 -2.05 -3.18 Tiles V & B, Blank Test 75, 345, 84-101-1

Example 2 A solution of ruthenium chloride is buffered with sodium acetate at pH 1.5 and is adjusted to 6% by weight of ruthenium.

Following the above-described cooking and applying process, the following chromatic values are obtained on the tile surfaces: L * a * b * V & B tiles, test No. 3 31, 64 -1.26 -4, 37 V & B tiles, test No. 4 32, 13 -1.41 -4.15 V & B tiles, test No. 5 31, 31 -1.01 -4.64 V & B tiles, white 75, 345, 84-103

Lisbon, November 27, 2000

THE OFFICIAL AGENT OF INDUSTRIAL PROPERTY

Claims (7)

\ Aqueous solution of ruthenium chloride for coloring ceramic black surfaces, characterized in that it is buffered with sodium and / or potassium acetate or propionate at a pH value of at least 1.5. A solution according to claim 1, characterized in that the solution is buffered to a pH value above 2.0. A solution according to claims 1 or 2, characterized in that the concentration of ruthenium salt is between 0.1 and 10% by weight, preferably 1 to 5% by weight. Solution according to one of Claims 1 to 3, characterized in that the solution additionally contains thickening agents. Process for the coloring of ceramic surfaces, characterized in that a solution according to one of Claims 1 to 4 is applied by spraying, dipping, painting or printing, drying and baking at a temperature of 300 to 1400 ° C, preferably from 800 to 1200 ° C, especially 1140 ° C, from half an hour to five hours, preferably from 1 to 2 hours, and by equalizing and polishing the surface of the ceramic pieces by grinding. A process according to claim 5, characterized in that the surface of the parts is watered and activated with water prior to application of the solution. Process according to claim 5 or 6, characterized in that the penetration depth of the solutions is increased by further treatment with water, before the pieces are dried and cooked. Lisbon, November 27, 2000 THE OFFICIAL AGENT OF INDUSTRIAL PROPERTY V JV \ - -2-